In a conventional baler, as shown for example in U.S. Pat. No. 4,106,267, hay, straw, silage or similar crop material that has been previously cut, windrowed or swathed, is picked up from the ground by a pick-up unit, fed into a duct by a packer unit and loaded in successive batches or charges into an elongated bale chamber by tines of a stuffer unit in timed sequence with a reciprocating plunger. The plunger compresses the material into bales and, at the same time, gradually advances the bales towards the outlet of the bale chamber. As the bales reach a predetermined length as determined by a metering device, a knotter device is actuated which wraps cord, twine or other flexible binding material around the bale and secures the ends of the binding material together. Instead of a packer unit it is also known to use for example a rotor cutter unit which chops the crop material into smaller pieces.
The packer or rotor unit pre-compresses the crop material in the precompression chamber against a backstop formed by the plunger, when closing off the entrance of the bale chamber. The stuffer unit is designed to transfer charges of the crop material quickly into the bale chamber within the short interval during which the reciprocating plunger clears the entrance of the bale chamber. Typically this is accomplished by a fork assembly of which the arms are rotatably connected to cranks, the arms being provided with longitudinally extending slots in which stationary journals are received. A uniform revolution of the cranks makes the arms shift along and pivot about the journals so that the tines of the fork travel along a generally kidney-shaped path with a varying speed. The maximum or peak speed is obtained when the distance between the connection to the cranks and the stationary journals reaches its minimum, since the arms then act as levers with very close fulcrum points. Such a system permits a quick sweep of the material behind the packer unit through the duct and to the entrance of the bale chamber.
This type of stuffer unit was originally designed for the baling of dry, low density material such as straw or hay, but meanwhile there has been an important shift in agriculture from the use of hay to the use of silage. Silage grass can also be baled, but since it has a higher humidity, a higher density and generates higher friction forces with the walls of the precompression chamber than the other crop materials, the load on the components of the stuffer unit increases accordingly.
A stuffer overload protection, will be triggered if for example a plug of crop material is formed in the precompression chamber, especially during the baling of silage. A conventional protection is the use of a shear bolt assembly in the drive line of the stuffer unit. When the loads exceed the shear strength of the bolt, the stuffer is disconnected before its components are damaged. The shearbolt can be replaced relatively easy, but in certain cases it will not be possible to restart the normal operation of the baler as the stuffer unit will not be able to remove the crop material in the precompression chamber without activating the overload protection. In this case it will cost the operator valuable time to render the baler operable again, because it will be required to clear the precompression chamber manually before the baler can be restarted. Furthermore this is a job that requires extensive safety precautions and it is very difficult to gain access to the intake duct of the precompression chamber.